Friction welding processes are utilized for mounting blades of carriers such as, for example, disks (blisks) for gas turbines. The carriers generally comprise an at least partially conically fashioned circumferential surface. A plurality of projecting humps uniformly spaced from one another can be provided at the circumferential surface of the carrier. The humps have welding surfaces at their end faces to which a respective blade is welded as an integral component part. The welding surfaces of the carrier and of the blades are pressed together with a compressing force for generating the necessary welding temperature, so that the joint zones or welding planes are heated up to the welding temperature during oscillating/linear relative motion of the blades relative to the carrier. When the welding temperature is reached, compression (axial longitudinal shortening) occurs in the parts to be joined (friction and compression phase).
For achieving good joint qualities, the compression should be distributed between both parts. Depending on the application, compression parts of the same size, or deviating from one another, are desired for the humps of the carrier on the one hand and the blades on the other hand. The compression portions, however, can partly differ greatly due to different thermal strengths of the participating materials and/or different heat elimination conditions as a result of different component part geometries that lead to different temperature profiles in the environment of the welding plane.
In friction welding of what are referred to as blisks for jet engines, titanium (Ti) materials are in fact generally utilized both for the carrier as well as for the blades. However, the two parts can comprise geometries differing from one another, for example, due to a cuboidal fashioned shoulder at the foot of the blade that is required for a clamp mechanism. As a result thereof, different heat illumination conditions and, thus, different temperature profiles in the environment of the welding zone arise that can lead to compression (crushing) parts deviating greatly from one another. When a compression (crushing) part is too low, correspondingly little welding bead is abraded out during the welding process, and contaminants, oxygen-rich inclusions or the like can remain in the welding zone and lead to poorer joint qualities.
In view of the joint quality, a problem is also that highly divergent temperature profiles can occur during the cooling at the end of the friction and compression (crushing) phase of the welding process in the welding zone as a consequence of different volume/surface conditions in the environment of the welding zone. This can lead to unfavorable stresses or edge errors in the joint zone and can reduce the joint quality. The different volume/surface conditions result from the welding surface that is oblong in cross-section and tapers comparatively acutely in the region of the front and back edges of the blades. As a result, small volumes of material are surrounded by large surfaces in the edge regions compared to the middle region.
European patent document no. 376 874 discloses a method for replacing a running blade of a rotor integrally provided with blades, and also discloses a method for the manufacture thereof. A respective blade is welded to a projecting stub of a rotor disk by pressing the blade against the stub and heating the connecting location to raise the stub and the blade to a temperature that effects softening, metal flow and joining, and that should lie in the range from 1038.degree. C. through 1149.degree. C. An initial heating for improving the joint quality and for avoiding voids in the welding zone is not discussed.
German patent document no. 695 00 234 T2 discloses a method for welding two blade parts, particularly a blade and the connector of a disk that are provided with a thickness at the front and back edge of the blade for improving the weld quality in the production of new parts. Since, given a repair, the connector already has the dimension of the final product, the welding zone is enlarged during repair not with an excess thickness but with a collar such as a lamina. The collar can be placed between the surfaces or proceed around them and is heated during welding to welding temperature and becomes molten, so that its residues must be subsequently removed. One disadvantage is that additional material is required that must be adapted to each of the blade parts. Furthermore, the collar must be adapted to the shape of the welding zone given modification thereof and, since it is not an integral component part, must be attached thereto before the welding.